(1) Field of the Invention
The present invention relates to a control apparatus and a control method of a variable valve timing structure for varying the opening/closing timing of an intake valve and/or an exhaust valve by changing the rotational phase of a cam shaft in an internal combustion engine.
(2) Related Art of the Invention
In the prior art, a variable valve timing structure for advancing or delaying the opening/closing timing of an intake valve and/or an exhaust valve by changing the rotational phase of the cam shaft was known (refer to Japanese Unexamined Patent Publication 7-233713, Japanese Unexamined Patent Publication 8-246820 and the like).
In the case where said variable valve timing structure is of a hydraulic type, with a structure where hydraulic pressure is controlled by controlling the duty of the current provided to a linear solenoid valve, the structure may be formed to limit the change of said rotational phase corresponding to the increase or decrease of the ON duty (current) by a stopper. For instance, when the stopper position (for example, the most advanced angle side) for limiting the change of rotational phase corresponding to the increase of the current is set as the target rotational phase, it was common to provide a 100% ON duty (maximum current) in order to move the rotational phase rapidly to said stopper position.
However, in the prior art, when the target rotational phase was set at said stopper position, the structure provided said 100% ON duty continuously even after the actual phase has been changed to the stopper position, which caused problems such as large power consumption and rising of coil temperature in the linear solenoid valve.